Nokia N1 running slow

Everything was perfect back then. However, after upgraded to android 5.1.1 the overall perfomance isn't as sleek as it used to be anymore. Apps like tumblr load slower, and time needed to turn on the device went longer ( phrase like "optimizing Z launcher for you" is seen ).
And latest version of instagram couldn't be launched, all you get is flash and then you're back on your homescreen . Only a version from year 2015 installed using apk would work, and it doesn't work well. Device would freeze and reboot spontaneously while using instagram. Is that got something to do with the incompatibility of X86 processor and the app ?
Anyone owning the device and found the solution? Your share would be very much appreciated , thanks !